1. Cross Reference to Related Applications
Not applicable.
2. Field of the Invention
The present invention relates generally to sludge load out gates, and more particularly to a gravity flow sludge load-out metering gate.
3. Discussion of Related Art
It is increasingly important for wastewater treatment facilities to provide an efficient and accurate system for sludge load-out. Because numerous methods have been devised to render biological sludge generally pathogen free and suitable for reuse as soil amendment and fertilizer, there is now a large demand for treated, dewatered biosolids, particularly by fertilizer manufacturers. Further, because large and small municipalities and sewage districts have high sewage throughput and limited sludge storage capacity, the accumulation of sludge inventory cannot be tolerated. Accordingly, it is imperative to have a sludge handling system that enables rapid load out into containers for transport either to sludge customers or to disposal sites.
Such a system must provide for rapid sludge load-out with a high degree of accuracy. Rapidity is simply a summary way of stating an arithmetical fact: that in a municipality with high sewage throughput, numerous trucks must pass through sewage treatment facility load-out stations each day to handle the sludge inventory. As a practical matter, the load-out system must enable the loading of a standard eighteen-wheel container truck within only a few minutes. In itself, this would not pose much of a problem, inasmuch as sludge storage hoppers could be designed with delivery orifices that would effectively dump their contents into a truck""s container. However, the load out must also be accurate in several senses. The accuracy must range over both the measurement of sludge delivered and the actual delivery, or load-out, of the sludge into container trucks. It must be measured accurately because municipalities must charge customers for sludge actually delivered, and there is no practical means for measuring sludge on the customer""s end of the transaction. It must also be loaded out in a controlled fashion into the container trucks because trucks are levied a fine or surcharge for overweight loads. Finally, it must be loaded out accurately because the sludge is classified as a hazardous material and cannot be carelessly splashed and splattered in delivery. The present invention addresses the need to load-out sludge in a rapid, but controlled fashion.
A principal concern in controlling sludge load-out is handling sludge of widely varying viscosities. Viscosity fluctuations are largely unavoidable and are caused by batch variants in sludge dehydration and temperature and varying material heights, causing variable head pressure in the loading hoppers. It would therefore be desirable to provide a sludge hopper gate having a variable load-out orifice to permit fine control of the sludge flow so as to minimize splattering and sludge loss.
Accordingly, it is an object of the present invention to provide a gravity flow sludge load-out metering gate that permits highly controlled loads-out of large volumes of sludge.
The gravity flow sludge load-out metering gate of the present invention is adapted for use in any sludge load-out station where dewatered biosolids are stored and then loaded-out from storage hoppers. The metering gate may be used in either an automated or a manual system. sequence. The metering gate comprises a substantially rectangular frame having longitudinal and horizontal frame rails and a transverse rail member which defines a gate front portion and a smaller gate rear portion.
Positioned above the front portion is a sludge inlet funnel that is inserted into the interior of a hopper discharge outlet. In a first embodiment, the sludge inlet funnel has a substantially square upper perimeter and has eight triangular, tapering interior sides. When viewed from above the sides define an asymmetrical eight-sided passage having four vertices at the upper comers of the inlet funnel and having lateral edges depending downwardly from the upper corners of the inlet funnel to define an asymmetrical diamond-shaped sludge discharge orifice. This asymmetrical diamond-shaped discharge orifice is highly effective in providing tight control over gravity fed sludge flow at various sludge viscosities, thereby giving greater control over the discharge trajectory, a reduction in splashing and splattering, and the ability to load out under a higher head of sludge. Just as importantly, it prevents the accumulation of sludge in xe2x80x9cdead spotsxe2x80x9d that will impede flow and require regular clearing and maintenance. In another embodiment, the sludge inlet funnel forms a symmetrical discharge orifice when viewed from above, and in combination with the load-out gate, described below, the symmetrical diamond-shaped discharge orifice is equally effective in providing control over the load-out process.
Interior to the metering gate frame is a substantially square metering gate blade, slidingly positioned above a plurality of support rollers, and having wings at each side passing through a slot which runs substantially the entire length of the rear portion of the each of the longitudinal frame rails. The slots acts as a metering gate blade guide during operation. The wings are operatively connected to the piston""s two hydraulic, electric, or pneumatic cylinders positioned at the side of the longitudinal frame rails. Movement of the metering gate blade is powered either manually or by an electric, hydraulic, or pneumatic system. When hydraulically or pneumatically powered, the gate movement is controlled by an assembly of isolation and solenoid valves comprising a manifold from which lines direct pressurized fluid or gas to inlet valves at both ends of the cylinders. Proximity switches at each end of at least one cylinder are electronically coupled via interconnecting cables to a PLC and provide precise gate position information to the metering gate operator or automatic system.